This invention relates to the preparation of alkanol alkoxylates via the catalyzed addition reaction of alkylene oxides with alkanols. More specifically, this invention is directed to a process for the preparation of an alkanol alkoxylate which comprises the reaction of an alkanol with an alkylene oxide in the presence of a basic calcium-containing catalyst and the neutralization of the resulting reaction mixture with an organic acid of critical definition.
Alkanol alkoxylates (or simply alkoxylates, as the terminology is alternatively applied herein) are known materials having utility, for instance, as solvents, surfactants, and chemical intermediates. Alkoxylates in which the alkyl group has a number of carbon atoms in the detergent-range, i.e., from about 8 to 20, are common components of commercial cleaning formulations for use in industry and in the home.
Under conventional practice, alkoxylates are typically prepared by the addition reaction of alkylene oxides with alkanols. In the particular case of the preparation of an ethoxylate (represented by formula III below) the addition of number (n) of ethylene oxide molecules (formula II) to a single alkanol molecule (formula I) is illustrated by the equation ##STR1## wherein R is alkyl and n is an integer equal to or greater than one. The product of such an alkoxylation reaction is a mixture of various alkoxylate molecules having a variety of alkylene oxide adducts, i.e., a mixture of compounds with different values of n.
Alkoxylation reactions between alkylene oxides and alkanols are known to be necessarily carried out in the presence of a catalyst, which may be either of acidic or, preferably, basic character. Suitable basic catalysts are recognized to include the soluble basic salts of the alkali metals of Group I of the Periodic Table, e.g., lithium, sodium, potassium, rubidium, and cesium, and the soluble basic salts of certain of the alkaline earth metals of Group II, e.g., barium and strontium.
With particular regard to calcium-containing catalysts as are employed in the process of this invention, the published European patent application Nos. 26,544, 26,546, and 26,547 describe alkoxylation reactions catalyzed by soluble basic calcium compounds. U.S. Pat. No. 4,302,613 describes the use of certain calcium compounds as co-catalysts in alkoxylation reactions.
Following an alkoxylation reaction carried out in the presence of a soluble catalyst, it is generally necessary to neutralize the reaction mixture, typically to a pH of about 5.0 to 7.0 by addition of an organic acid. Neutralization is required because a quantity of base sufficient to catalyze the alkoxylation would, if it remained unneutralized, promote chemical instability in the product. Under conventional commercial practice, acetic acid is utilized in essentially all cases for catalyst neutralization during preparation of alkoxylates.
The preparation of alkoxylates via the reaction between alkanols and alkylene oxides catalyzed by soluble, basic calcium catalysts, while not now commercially practiced, is of particular advantage for several reasons, including the characteristic narrow-range distribution of alkylene oxide adducts in the alkoxylate product molecules, the activity and selectivity of the catalysts, and the negligible toxicity of the catalysts and catalyst residues. However, it is now observed that when neutralized with acetic acid the calcium-containing alkoxylation reaction mixture is a product having physical properties unacceptable for many applications. In combination (and in the presence of the alkoxylate) even relatively small quantities of the calcium ion and the acetic acid interact to produce a semi-solid or gel-like alkoxylate product of high viscosity. The handling properties of this product are in sharp contrast to those of the liquid products of common conventional alkoxylation processes, and are of substantial disadvantage in storage, transportation, formulation, and application to detergent and other services. Accordingly, a process for the preparation of a neutralized alkanol alkoxylate product of low viscosity, from C.sub.8 to C.sub.18 alkanols and C.sub.2 to C.sub.4 alkylene oxide via a calcium-catalyzed alkoxylation reaction, would be most desirable.